In a gas turbine engine, hot combustion gases generally may flow from one or more combustors through a transition piece and along a hot gas path of a turbine. A number of turbine stages typically may be disposed in series along the hot gas path so that the combustion gases flow through first-stage nozzles and buckets and subsequently through nozzles and buckets of later stages of the turbine. In this manner, the nozzles may direct the combustion gases toward the respective buckets, causing the buckets to rotate and drive a load, such as an electrical generator and the like. The combustion gases may be contained by circumferential shrouds surrounding the buckets, which also may aid in directing the combustion gases along the hot gas path. In this manner, the turbine nozzles, buckets, and shrouds may be subjected to high temperatures resulting from the combustion gases flowing along the hot gas path, which may result in the formation of hot spots and high thermal stresses in these components. Because the efficiency of a gas turbine engine is dependent on its operating temperatures, there is an ongoing demand for components positioned along the hot gas path, such as turbine buckets, to be capable of withstanding increasingly higher temperatures without failure or decrease in useful life.
Certain turbine buckets may include one or more passages defined within the turbine bucket for cooling purposes. For example, cooling passages may be defined within the airfoil, the platform, the shank, and/or the tip shroud of the turbine bucket, depending on the specific cooling needs of the bucket, as may vary from stage to stage of the turbine. According to certain configurations, the cooling passages may be defined within regions near a hot gas path surface of the turbine bucket. In this manner, the cooling passages may transport a cooling fluid, such as compressor discharge or extraction air, through desired regions of the turbine bucket for exchanging heat in order to maintain the temperature of the regions within an acceptable range.
According to one known configuration, the turbine bucket may include a number of long, straight cooling passages each extending radially from the root end to the tip end of the turbine bucket. The cooling passages may be formed by various methods, such as drilling. However, root-to-tip cooling passages formed by drilling are limited to a straight path through the turbine bucket. Accordingly, variation of the three-dimensional shape of the turbine bucket, specifically the airfoil portion thereof, may be limited due to the need to accommodate a straight line of sight for each of the cooling passages extending radially therethrough and to maintain a minimum wall thickness. Moreover, placement of the straight cooling passages near a hot gas path surface, such as along the trailing edge of the airfoil, may be challenging due to the aerodynamic shape of the airfoil. Further, for longer turbine buckets, it may be particularly challenging and costly to drill the cooling passages through the entire length of the bucket, due to high length-to-diameter ratios of the passages.
According to another known configuration, the turbine bucket may include a number cooling passages each having two straight portions connected to one another. Specifically, a first portion may extend from the root end of the turbine bucket, while a second portion extends from the tip end of the turbine bucket to the first portion. The two straight portions of the cooling passage may meet within the platform of the turbine bucket or elsewhere. According to yet another known configuration, the turbine bucket may include a number of straight cooling passages each extending radially from the tip end of the turbine bucket to a cooling cavity defined within the shank of the turbine bucket. In this manner, the cooling passages are shorter than the length of the turbine bucket. Although these configurations may reduce some of the challenges associated with root-to-tip cooling passages, they still may significantly limit the three-dimensional shape of the airfoil, may limit the cooling effectiveness in desired zones, and may be challenging and costly to manufacture.
There is thus a desire for an improved turbine bucket having a cooling passage configuration for cooling the turbine bucket at high operating temperatures. Specifically, such a cooling passage configuration may allow the turbine bucket, specifically the airfoil portion thereof, to have various complex three-dimensional shapes or twist for improved aerodynamics. Such a cooling passage configuration also may allow for optimal placement of the cooling passages for targeted cooling of the limiting section of the airfoil, while also minimizing the cost and complexity of manufacturing the turbine bucket. Ultimately, such a cooling passage configuration may improve efficiency and performance of the turbine and the overall gas turbine engine.